Wireless functional testing of RFID tag

ABSTRACT

Wirelessly testing an RFID tag before it is packaged or otherwise entered into a process reserved for “working” RFID tags is described. Various processes that employ such wireless testing as well as various “on-die” RFID tag antennae designs for facilitating the wireless testing are also described.

FIELD OF THE INVENTION

The field of invention relates to the semiconductor chip arts; and, morespecifically, to the functional testing of an RFID tag

BACKGROUND OF THE INVENTION

RFID Tags

A Radio Frequency Identification (RFID) tag is a semiconductor chip(also referred to as a “die” or integrated circuit) that can positivelyrespond to a wireless signal sent by a “reader” that inquires into theRFID tag's existence. By positively responding to the reader's wirelesssignal, the RFID tag can verify its presence to the reader. Frequentlycited RFID tag applications include automated inventory managementsystems and automated transportation/distribution systems (e.g., apallet affixed with an RFID tag will be able to wirelessly identifyitself to an intelligent warehousing reader system so as to confirm itspresence within the warehouse).

The less expensive an RFID tag solution, the easier it is to justify theexpense of integrating RFID tag semiconductor chips amongst stocked ortransported goods. Therefore RFID tag solutions tend to be sensitive toproduction and/or implementation costs. One aspect that reveals the costsensitivity of an RFID tag solution is the integration of an RFID tag'santenna.

An RFID tag, being a wireless device, uses an antenna to receive thewireless signal sent by the reader. Generally, the larger an antenna,the more sensitive the antenna is. That is, the larger the antenna, themore apt it is to detect “weak” wireless signals such as those thatmight be sent by a distant reader. Therefore, in order to increase thecommunicative range between a reader its corresponding RFID tags, theRFID tags are each affixed with an antenna that is larger than the RFIDtag die.

FIG. 1 shows a simple depiction. According to the depiction of FIG. 1, apaper antenna 101 is affixed to an RFID tag 103 with conductive glue102. The paper antenna 101 is printed upon with conductive ink patternedin some fashion to form a working antenna. Electrical signals induced onthe antenna 101 flow through the conductive glue 102 and into the RFIDtag die 103. Because a paper antenna 101 is used, the RFID tag die 103itself does not contain an “on-die” antenna.

The paper antenna 101 dramatically reduces implementation costs whileallowing for an antenna size that is significantly larger than thesemiconductor die 103 size. In one implementation, the paper antenna 101is approximately a 10 mm×10 mm square and the die 103 is 1 mm×1 mmsquare.

Another RFID tag cost structure issue concerns the packaging of the RFIDtag die. An appropriate depiction is provided in FIGS. 2 a and 2 b. RFIDtags, being semiconductor chips, are manufactured on wafers where eachwafer contains many discrete RFID tag chips. The die 208 from a samesawed wafer are typically separated by channels 210 referred to as“sawed streets”, and, a layer of tape 209 beneath the sawed wafer 202keeps the die 208 in place. A robotic “pick-and-place” machine 201 picksindividual die from the sawed wafer 202 (e.g., using a suction cup orcollet 207) and places each picked die at a location 203 from where apackaging process may commence. Here, packaging can be any kind ofprocessing that a die is subjected to after it is picked (e.g.,integration into a hermetically sealed ceramic “single die” package,placement into a carrier with other die for shipment, etc.).

A typical “pick-and-place” machine generally exhibits movement 204, 205along at least two planes to “pick-up” the die and move it to anotherlocation.

If the RFID tag chips from a same wafer are not sufficientlyfunctionally tested so as to render a “pass” or “fail” disposition untilafter they have been diced from the wafer and individually packaged, theexpense of packaging the portion of chips that ultimately fail theirfunctional test is pure economic waste. Therefore it behooves the RFIDtag manufacturer to eliminate this waste through some kind of functionaltesting that takes place prior to the packaging of the individual die.

Die Seal Rings

A die seal ring is essentially a barrier that surrounds a semiconductordie's active device area in order to block the penetration ofcontaminants into the die's active device area. The active device areaof a die is the region of the die where most if not all of the die'stransistors are located. FIGS. 3 a through 3 c show prior art depictionsof a semiconductor die's die seal ring. FIG. 3 a shows a top view, FIG.3 b shows a cross-section and FIG. 3 c shows a three dimensionalperspective of a basic unit of the die seal's structure.

FIG. 3 a shows an RFID tag die 301 and its corresponding active devicearea boundary 302. A die seal ring 303 is observed surrounding theactive device area between the active device area boundary and the dieedge 303. FIG. 3 b shows a cross section of a region 304 ₁, of the dieseal ring observed in FIG. 3 a. According to the depiction of FIG. 3 b,the die seal ring is observed to be a stacked structure of metal wires312 ₁, 312 ₂, 312 ₃ “bar” vias 313 ₁, 313 ₂ and a “bar” contact 311.

FIG. 3 c shows a perspective view 314 of a continuous metal wire 312 anda bar via 313. Whereas a standard via can be viewed as a scalar “dot” ofmetal that runs through dielectric so as to provide vertical electricalcontact between two metal wires that run along different verticalplanes, as observed from FIG. 3 c, a bar via 313 is “continuouswire-like” and may run the length of the wires its provides electricalcontact between. A bar contact 311 is similar to a bar via with theexception that a bar contact provides electrical contact between thesemiconductor substrate 310 and a metal wire (whereas a bar via provideselectrical contact between vertically separated wires).

From FIGS. 3 a through 3 c, it is apparent that the die seal ringdepicted therein is a type of stacked metal structure that essentiallyforms a “solid wall of metal” that surrounds the active device area. Thesolid wall of metal preserves the structural integrity of the activedevice area's features by preventing external contaminants from reachingthe active device area laterally. FIGS. 3 a and 3 b only show threelevels of metal wiring. It should be understood that die seal rings ofmore or less than three levels of metal wiring can be implementeddepending on the type of semiconductor manufacturing process. Typically,a die seal ring will extend through each metal wiring layer used withinthe RFID tag's active device area.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which likereferences indicate similar elements and in which:

FIG. 1 (prior art) shows a paper antenna attached to an RFID tag;

FIG. 2 (prior art) shows a pick-and-place machine;

FIG. 3 a through 3 c (prior art) show a die seal ring structure;

FIG. 4 a shows an embodiment of a methodology in which an RFID taghaving an “on-die” antenna is functionally tested in wireless fashionover the course of its transport between different locations;

FIG. 4 b shows a flow diagram that corresponds at least to theembodiment of FIG. 4;

FIG. 4 c shows an embodiment of a methodology in which an RFID taghaving an “on-die” antenna is functionally tested in wireless fashionduring pick-and-placement;

FIG. 4 d shows an extension of the methodology of FIG. 4 c in which atested RFID tag may be placed in a passed bin, a failed bin or amarginally passed bin;

FIG. 4 e shows an extension of the methodology of FIG. 4 c in which atested RFID tag that has passed its functional testing is moved from apassed bin to a carrier from where packaging of the RFID tag maycommence;

FIG. 4 f shows an extension of the methodology of FIG. 4 c in which apick-and-place machine is shown;

FIG. 4 g shows an extension of the methodology of FIG. 4 f in which atester is shown being integrated with the pick-and-place machine;

FIG. 4 h shows a depiction of a functional tester's antenna beingcoupled to a pick-and-place machine;

FIG. 5 shows a depiction of an RFID tag in the grasp of a machine beingtested through an air medium;

FIG. 6 a top view of an RFID tag having an on-die antenna;

FIG. 7 shows a top view of an RFID tag having an on-die antenna that iselectrically isolated from the RFID tag's die seal ring;

FIG. 8 a shows a first embodiment of a cross section of a region of FIG.7 where electrical contact between the on-die antenna and the activedevice area is made;

FIG. 8 b shows a second embodiment for making electrical contact betweenthe on-die antenna and the active device area;

FIG. 9 shows a top view of an RFID tag having an on-die antenna that iselectrically integrated with an effective RFID tag die seal ringstructure;

FIG. 10 shows a cross section of a region of FIG. 9;

FIG. 11 shows a cross section of a region of FIG. 9;

FIG. 12 shows a dipole on die RFID tag antenna.

DETAILED DESCRIPTION OF THE INVENTION

Recalling from the description in the Background that prior art RFIDtags have not been designed with integrated “on die” antenna (becausethe size of the antenna is not large enough to detect signals fromdistant readers); and, that functional testing of an RFID tag prior toits packaging would help reduce the manufactured cost of an RFID tag die(because a “bad” die could be identified before expending the cost ofits packaging); then, a solution is to design an RFID tag with anintegrated “on die” antenna for purposes of functionally testing the dieprior to its packaging. Here, an “on-die” antenna is an antenna that ispart of the integrated circuitry of the RFID tag formed with thesemiconductor manufacturing process used to manufacture the RFID tagitself.

Moreover, certain types of business and/or technology models may involvethe shipment of working die that have not been packaged into a discrete“per die” packages (e.g., a ceramic casing having leads or other type ofelectrical “I/O”). Here, the ability to screen functional vs.non-functional individual, unpackaged die is important because suchscreening could be used to prevent the shipment of non-working die.Moreover, certain types of business models may not require the use of apaper antenna. That is, only “short range” listening capability isrequired between the RFID tag and the reader, and, an-die antennae hassufficient range to meet the desired performance objectives. RFID tagschosen for such applications should be functionally testable withoutapplication of an external antennae.

FIGS. 4 a and 4 b show, at a high level, the wireless testing of anindividual RFID tag (i.e., the testing of an RFID tag where one or moretest signals are sent through an air-medium) so that a functionaldisposition can be made on the RFID tag (e.g., “pass” or “fail”). Here,an individual RFID tag is grasped 1 and functionally tested 2 through anair medium. If the RFID tag passes the functional testing 3 a it isplaced in a “pass” bin 401. If the RFID tag fails the functional testing3 b it is placed in a fail bin 402. By treating RFID tags placed in the“pass” bin 401 as having successfully yielded their manufacturingprocess (e.g., through shipment and/or packaging), and, by treating RFIDtags placed in the “fail” bin 402 as having not successfully yieldedtheir manufacturing process, certain economic wastes can be avoided.

In order to test an individual RFID tag, the RFID tag should beseparated from the other die manufactured on the same wafer as the RFIDtag. FIGS. 4 b and 4 c describe not only the wireless testing of anindividual RFID tag prior to any treatment based on its functionaldisposition, but also, separation of the die from its correspondingwafer beforehand. According to FIG. 4 b a wafer is initially fabricated410, and, after its fabrication, the wafer is sawed 411.

Then, referring to FIGS. 4 b and 4 c, an individual RFID tag is picked403 (e.g., from the sawed wafer 404 itself) and wirelessly tested 412.If the RFID tag passes its functional testing its placed in a “pass” bin413. If the RFID tag fails its functional testing, the RFID is placed ina “fail” bin 414. The process repeats for each die from the wafer 415.Again, die placed in the pass bin can be given further appropriatetreatment (e.g., direct shipment, packaging, etc.). RFID tags placed inthe “fail” bin are effectively prevented/screened from being given suchtreatment and, according to at least one approach, are discarded.

FIG. 4 d shows an extension to the approach of FIG. 4 a in which thefunctional test disposition has three possible outcomes: “pass”, “fail”,and “marginal pass”. Here, a marginal pass 405 could be given to anindividual die having one or more tested characteristics that falloutside a specified “passing” range. A marginally passing RFID tag isplaced in a “marginal pass” bin 406 from where some kind of treatment,other than being immediately scrapped (e.g., as in the case of a “fail”)and other than being unconditionally sent forward (e.g., as in the caseof a “pass”).

For example, RFID tags submitted to the “marginal pass” bin 406 may beidentified as being suitable only for a limited number of applications(e.g., low performance applications where the reader is specified toexhibit a strong output signal and/or is specified to be placed close tothe RFID tag) whereas RFID tags submitted to the “pass” bin have norestrictions placed as to which application they may be placed in.Essentially, where more than two test results are possible themanufacturer has the ability to grade yielded die (e.g., A, B, C, etc.),where, typically, more restrictions are placed on the usage of die givena lower grade than die receiving a higher grade.

FIG. 4 e shows an extension of the approach of FIG. 4 a in which RFIDtags deemed to be “passing” are sent forward to a packaging process 407.The commencement of the packaging process 407 may involve placement ofthe RFID tag on a run of tape or on a die carrier 408. In a furtherapproach, “passing” RFID tags are placed directly in a location fromwhere the packaging process 407 may commence (e.g., by being placeddirectly on the tape/carrier 408 by a pick-and-place machine thattransports the die while it is being functionally tested).

FIG. 4 f shows an implementation where the RFID tag is physically in thegrasp of a pick-and-place machine 409 while the RFID tag is beingfunctionally tested through an air medium. Here, it should be understoodthat the approach of FIG. 4 f may be performed in conjunction with anyone or more of FIGS. 4 a through 4 e. That is, the functional test mayoccur while an RFID tag is being transported (i.e., travels along somekind of trajectory (where a trajectory is understood to mean a “path”that is linear, curved and/or otherwise)) to a location by apick-and-place machine 409. According to a further approach, thepick-and-place machine 409 picks an RFID tag from amongst diemanufactured on the same wafer (e.g., the pick-and-place machine 409picks the RFID tag from a sawed wafer) and wirelessly tests the diebefore a decision is made as to where the RFID tag is to be placed basedupon the results of the functional testing (e.g., pass bin, fail bin,marginal pass bin, tape/carrier, start of packaging process, etc.).

FIG. 4 g shows the coupling of a functional tester 416 to apick-and-place machine 409 in order to effect wireless functionaltesting. FIG. 4 h shows that the antenna 417 used for wirelessly testingan RFID tag that is in the grasp of the pick-and-place machine 409 maybe physically coupled to the pick-and-place machine 409.

According to one embodiment, a picked die is deliberately tested at alocation where the remaining non picked die manufactured from the samewafer 302 cannot suitably detect the wireless signals from thefunctional test equipment. Here, manufactured RFID tag die may containhardwired “initial” identification codes that repeat over the surface ofthe wafer (e.g., every reticle). As such, if any of the yet-to-pickeddie could detect the wireless signaling from the functional testequipment, multiple die that respond to the same identification codemight simultaneously respond to a functional test intended to beadministered to a single die having the identification code.

Moreover, an RFID tag is typically designed to convert energy from areceived wireless signal into the electrical power that drives the RFIDtag's transistors. Here, if the yet-to-picked die from a same wafer wereto detect the functional tester's wireless signal, and if such die werenot yet separated from one another (e.g., their region of the wafer hadnot yet been sawed), it could result in the “power-up” of a large numberof these die.

FIG. 5 shows an implementation where the transmitting antenna 502 forthe functional tester (which may or may not be affixed to thepick-and-place machine 501) being located a small distance 504 from adie 503 that is in the grasp of the pick-and-place machine 501. Here,over the time period in which a picked die is functionally tested: 1)the transmitted power of the wireless signal from the functional testerantenna 502 should be small enough; 2) the distance 504 between thefunctional tester antenna 502 and the die 503 under test should be smallenough; 3) and the distance between the functional tester antenna 502and the yet-to-picked die (not shown) should be large enough—suchthat—the die 503 under test detects the functional tester's wirelesssignal but each die yet-to-picked does not detect the functionaltester's wireless signal.

Recalling from the discussion in the Background that smaller antennasize results in lower antenna sensitivity, note that an on-die antennawill have less sensitivity than a larger paper antenna (because of thesmall size of the RFID tag die); which, in turn, results in the abovedescribed implementation goals being achievable. Specifically, owing tothe lower sensitivity on-die antenna, the yet-to-picked die will not beable to detect the functional tester's wireless signal—particularly ifthe die under test 503 is located at the time of its testing close tothe functional tester antenna 502 and the wireless signal emanating fromthe functional tester antenna 502 is of a sufficiently low power. Thefunctional tester antenna 502 may be affixed to (or otherwise integratedwith) the pick-and-place machine; or, may simply be placed proximate tothe pick-and-place machine.

FIG. 6 shows a high level depiction of an RFID tag die 601 having anintegrated on-die antenna 603 that is placed outside the RFID tag'sactive device area 602. Placement of the antenna 603 outside the activedevice area 602 allows for simpler design (because the antenna wiring isessentially separated from the wiring of the RFID tag's primarycomponents); and, moreover, yields an antenna having sufficient size tobe sensitive to the functional tester's wireless signal. Also, placementof the “on-die” antenna outside the RFID tag's die-seal ring preventsthe die-seal ring from shielding the antenna from the wireless signal itis supposed to receive.

Possible RFID tag “on-die” antenna designs are discussed immediatelybelow with respect to FIGS. 7 through 11. Recall from the backgroundsection the discussion concerning RFID tag die seal rings. FIGS. 7 and 8a, 8 b depict design embodiments where the on-die antenna iselectrically isolated from the die's die seal ring. By contrast, FIGS.9, 10 and 11 depict design embodiments where the on-die antenna isstructurally and electrically integrated with the RFID tag's die sealring. The die seal ring of the embodiments depicted in FIGS. 7 and 11can be implemented as a traditional die seal ring. By contrast the dieseal ring of the embodiments depicted in FIGS. 9 and 10 are nontraditional in the sense that the die seal ring “loops around” theactive device area (to construct an antennae). An additional on-dieantenna design embodiment is depicted in FIG. 12.

FIG. 7 shows an integrated on die antenna 804 whose corresponding wiringruns substantially outside the die seal ring 703 of an RFID tag die 701.As discussed in the Background, the die's deal seal ring 703 surroundsthe die's active area 702. The antenna wiring 704 is depicted as a coilthat spirals around the die's die seal ring 703. Spiraling a continuouslength of wiring multiple times around the die's die seal ring 703corresponds to an extended antenna wire length. Here, the longer theantenna wire length the greater the sensitivity of the antenna.

Recalling the discussion above concerning the sensitivity of theintegrated on-die antenna, an antenna of appropriate sensitivity for aparticular application can be particularly designed for by coiling theantenna wire for an appropriate number of turns. In one embodiment, theantenna wire length runs for approximately four full turns around theactive device area of a 1 mm×1 mm die (i.e., approximately 16 die edgelengths=16 mm wire length).

According to the design implementation of FIG. 7, the antenna wiring 704is isolated from the die's die seal ring 703. A first embodiment of thecross section of region 705 of FIG. 7 is shown in FIG. 8 a todemonstrate not only an exemplary cross section of the antenna wirecoils 704, 804 but also a design for making electrical contact betweenthe antenna wiring 704, 804 and a node within the active device area702, 802, where, again, the die's die seal ring 703, 803 surrounds theactive device area 702, 802 and is electrically isolated from theantenna wiring 704, 804.

According to the depiction of FIG. 8 a, each of the antenna coils 804are constructed similarly to the die seal ring 803. That is,essentially, a solid wall of metal formed with metal lines, bar vias andbar contacts. In a sense, the cross section “looks like” multiple dieseal rings. The innermost antenna coil 8041 from the die edge 801 (i.e.,the antenna coil 804 ₁ closest to the die seal ring 803) is electricallycoupled to a metal wire 806 within the active area 802 through aconductive channel that includes regions 807, 808 doped similarly tosource/drain regions and a well 811 that is formed within thesemiconductor substrate 810.

According to the specific implementation observed in FIG. 8 a, an Ndoped well 811 formed within a substrate 810 is part of the conductivechannel. The conductive channel also includes N+ doped regions 807, 808beneath the contact metal 813 of antenna coil 804, and active regionwire 806, respectively. The conductive channel is isolated from the dieseal 803 by way of a P+ doped region between the N well 811 and the dieseal contact metal 814. The P+ region corresponds to the anode of areverse biased diode that essentially forms the electrical isolationbetween the conductive channel 811 and the die seal ring 803. Trenchisolation regions 812, through 8124 are part of the exemplary applicablesemiconductor process and help thwart lateral current flow near thesemiconductor substrate surface.

FIG. 8 a also shows a layer 815 between the embedded conductive channellayer 811 and the bulk substrate 810. Here, the presence of layer 815forms a pair of PN junctions (one at the layer 811/layer 815 interfaceand one at the layer 815/layer 810 interface). The pair of PN junctionsessentially forms a vertical bipolar transistor whose base (layer 815)is “open circuited” so that the transistor is permanently “off” so as toprevent current flow in either direction between the conductive channel811 and the bulk substrate 810. Here, if bulk substrate region 810 weredoped N type, layer 815 would be doped P type and well 811 would bedoped N type as depicted in FIG. 8 a. Conversely, if substrate region810 were doped P type, layer 815 would be N type, the well 811conductive channel would be doped P type and regions 807 and 808 wouldbe degenerately doped P type (i.e., P+). In order to properly form thereverse biased diode between the N well 811 and the die seal ring (i.e.,the P+ region of FIG. 8 a) would be replaced by a P+/N region so that avertical P+/N/P structure exists (where the P region is well 811). Moredetails regarding isolation between the antenna node and the substrateare provided with respect to FIGS. 10 and 11.

FIG. 8 b shows another approach that is compatible at least with Copper(Cu) metallurgy based manufacturing processes (i.e., manufacturingprocesses where the interconnect wiring is formed substantially withCu). In Cu based processes (and possibly other Damascene processes) aconductive “capping” layer is formed over the highest layer of Cu basedwiring in order to prevent the corrosion of the Cu based wiring. Thecapping layer is typically made of a non corrosive metal such asAluminum (Al). Thus, referring to FIG. 8 b, metal wires ⁸²⁵, through8253 correspond to the highest layer of wiring based on Cu.

The capping layer is show in FIG. 8 b as MCAP layer 827. MCAP layer 827straddles over the die seal ring 823 (noting that the die seal ringincludes metal wire 825 ₂), supported or at least separated from the topof the die seal ring 825 ₂ by a layer of dielectric 8262, andelectrically couples a wire 825 ₁ associated with the on die antenna anda wire 8253 within the active device area. Thus, according to thisstructure, the “conductive channel” runs over the die seal ring ratherthan beneath the die seal ring as described with respect to FIG. 8 a.

FIG. 9 shows another, alternative implementation in which the antennawiring and die seal ring are structurally and electrically integratedwith one another 904. Following the coil structure 904 of FIG. 9, notethat an “absolute boundary” between the active device area 902 and thedie edge 901 does not exist. That is, unlike the approach of FIG. 7, apath exists from the die edge 901 to the active device area 902 thatdoes not cross a metal barrier. The integrated approach of FIG. 9 shouldresult in smaller die size as compared to the non integrated approach ofFIG. 7; which, in turn may result in lower per RFID tag production cost(because more RFID tags can be fabricated on a single wafer of silicon).

FIG. 10 shows a cross section of region 905 of FIG. 9. Comparing FIGS. 9and 10, note that the innermost antenna wiring coil 1041 is coupled to awire 1006 that runs directly into the active device area 1002. Hence,the coupling between the antenna and the active device area is made bystraightforward interconnect metal rather than a conductive channel thatruns above or below a traditional die seal ring. Nevertheless, theantenna wiring is effected (particularly with coil wires 1004 ₂ through1004 ₄) with die-seal like structures (i.e., a stacked structure thatincludes a bar contact, bar vias and continuous interconnect wiring).

Because of the die-seal like structures used to construct the antennacoil wiring 1004, a good degree of structural preservation will still beimposed upon the features of the active device area. A conceivablefailure mechanism is the introduction of a contaminant that is able tomigrate “around-and-around” the open path from the die edge 1001 to theactive device area 1002. Exposure to such a failure mechanism may beaccounted for on a product-by-product basis (i.e., for some products theexposure may be acceptable while for others it may not be).Alternatively the exposure may be reduced through design such as, forexample, passivating the die with a substance (e.g., wax) that serves asanother barrier to contaminants as compared to the traditionalpassivation materials (e.g., Siliconoxynitride SiO_(x)N_(y), SiliconNitride Si₃N₄).

FIG. 10 shows the substrate regions beneath the coil wires (such asregions 1007 ₁ and 1007 ₂ for coil wire 1004 ₄) having at least a pairof PN junctions situated to prevent current flow in either direction(i.e., from coil wire to substrate; and, from substrate to coil wire).Prevention of current flow can be accomplished by viewing the pair of PNjunctions as a pair of diodes and coupling the diodes such that theiranodes are connected together; or, their cathodes are connectedtogether. For example, if the wafer substrate 1009 is doped P type,region 1007 ₂ would be doped N type and region 1007 ₁ would be doped Ptype (alternatively, if the substrate 1009 is N type, region 1007 ₂would be doped P type and region 1007 ₁ would be N type).

Arranging the PN junctions as described above can also be viewed as avertical bipolar transistor. Here, the base region 1007 ₂ isintentionally left “open circuited” so that the transistor ispermanently “off”. Conceivably, additional pairs of PN junctions couldbe formed so that a pair of bipolar transistors each with an open baseare stacked on top of each other (e.g., in the case of a second bipolartransistor, each of layers 1007 ₁ and 1007 ₂ would “divide” into twolayers).

Here, in deciding the appropriate amount of coil wire/substrateisolation for any particular RFID tag design, consideration should begiven to any large voltages that may appear on the antenna wiring (e.g.,if an RFID tag with a large antenna may be placed close to a reader witha “strong” output signal). Alternatively, a DC bias may be applied tothe antenna wiring so that current flow need only be prevented in onedirection (e.g., from coil wire to substrate). In this case only asingle reverse biased PN junction may be formed. However, RFID tags aretypically designed such that the RFID tag die is powered from the energyreceived in the wireless signal received by the antennae. DC biasing ofthe antenna may be difficult or undesirable in these circumstances.

Regardless, if high antenna wiring voltages are not a concern and/or,owing to the electrical design surrounding the antenna, current flowbetween the die seal ring and substrate is only possible in onedirection, then, in either or both of these cases, only a singlereversed biased PN junction can be implemented (i.e., regions 1007 ₁ and1007 “collapse” into a single layer). Here the layer between the coilwiring and the substrate should be doped opposite that of the substrate.Lastly, note that trench isolation structures are also shown in FIG. 10(such as trench isolation region 1008) that act to thwart current flowlaterally at or near the surface of the substrate 1009.

FIG. 11 indicates that structures other than die-seal like structuresmay be used to implement one or more coil wires 1104. Here, it isrelevant to consider that a typical antenna is expected to propagatesignals having high frequency components, and, that impedance matchingis a consideration that should be taken into account. Impedance matchingis a high frequency design objective that strives to match the impedanceof a first component (e.g., the characteristic impedance of an antenna)with that of a second component (e.g., the input impedance of ademodulator or amplifier or filter), where, the two components arecoupled together and are expected to propagate high frequency signals.Failure to impedance match along a signal path can result in unwanted“reflections” that may corrupt the high frequency components of thereceived wireless signal.

As such, the characteristic impedance of the antenna wiring should beaddressed prior to finalizing its design. Those of ordinary skill willbe able to correctly determine the characteristic impedance of aspecific antenna wiring design. As such, a detailed discussion ofantenna impedance matching need not be presently discussed.Nevertheless, it is important to point out that—generally—antenna wiringmay be modeled with series inductance shunted on both sides by acapacitance. The specific inductance and capacitance values determinethe antenna's characteristic impedance and are themselves determined bythe physical layout of the antenna wiring itself.

Generally, the closer a pair of antenna wires are to one another thegreater the capacitance, and, the greater the vertical stacking heightof the antenna wiring the greater the capacitance. Here, the verticalstacking height of the antenna wiring is proportional to the number ofbar vias and metal lines that are observed if a cross section of theantenna wiring is observed. It is therefore apparent that those ofordinary skill will be able to craft antenna wiring structures otherthan those that mimic or closely resemble a die-seal structure.

FIG. 11 shows one such example where antenna coils 1104 ₂ through 1104 ₄are only single layer wires. Here, note that the specific structure ofFIG. 11 imposes a die-seal like structure at the inner most wire 1104 ₄from the die edge 1101. As such, structural integrity similar to thatprovided by a traditional die-seal should still be provided to theactive device area 1101.

Note that the particular embodiment of FIG. 11 follows the “top-down”design approach of FIG. 7, but, unlike the cross sections of FIGS. 8 aand 8 b in which the antenna wiring was electrically isolated from thedie seal ring, the cross section of FIG. 11 indicates that the die sealring is electrically coupled to the antenna wiring through wire element1110. Thus, like the approaches of FIGS. 9 and 10 (at least in theelectrical sense) the die-seal ring is integrated with the antennawiring itself. As such, there does not exist an embedded conductivechannel above or below the traditional die seal structure. Here, becausethe die seal ring is electrically coupled to the antenna wiring, an“off” bipolar transistor is also observed beneath the die seal ring byway of layers 1107 ₁ and 1107 ₂ (similar to layers 1007 ₁ and 1007 ₂ ofFIG. 10) in order to prevent current flow between the die seal ring andthe substrate 1109.

FIG. 12 shows another integrated “on-die” antenna design that may beused in the alternative to the coil approach discussed above. Theapproach of FIG. 12 generally may be viewed as a dipole antenna havingmetal lines 1204 ₁, 1204 ₂ that “serpentine” back and forth along sideone another off a side of the active device area. One or more regions ofthe antenna wire (e.g., one or more individual wire lengths that run thelength of the active device area edge) may be built with stackedstructures that mimic or resemble a die seal structure.

For simplicity no traditional die seal structure is shown in FIG. 12 (assuch, electrical contact between the antenna wiring and the activedevice area 1202 may be made through standard metal interconnect). Atraditional die seal structure may be implemented between the antennawiring and the active device area, in which case, a conductive channelthat runs above or below the traditional die seal structure such asthose described above with respect to FIGS. 8 a and 8 b. Alternatively,the die seal ring and the antenna may be shorted together where both areelectrically isolated from the substrate (e.g., as depicted in FIGS. 10and 11) by at least one reversed biased PN junction.

It should be understood that even though the term Radio Frequency (RF)in the acronym RFID tag can be construed to mean a specific frequencyrange (specifically, carrier frequencies within the RF range), ifwireless semiconductor chip identification tags are feasible having awireless frequency range that falls outside the RF range, then, term“RFID tag” should be understood to cover these identification tags aswell.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

1. A method, comprising: transmitting a wireless signal to an RFID tag, while said RFID tag's positioning is under the control of a machine that transports said RFID tag, to administer a functional test to said RFID tag, said RFID tag having an on-die antenna adapted to receive said wireless signal.
 2. The method of claim 1 further comprising: obtaining one of a plurality of possible results of said functional test; selecting a distinct location from amongst a plurality of distinct locations, said distinct location corresponding to said obtained result; placing said RFID tag in said distinct location.
 3. The method of claim 2 wherein said distinct location is where scrap RFID tags are placed, said RFID tag deemed to have failed said functional test.
 4. The method of claim 2 wherein said distinct location is where RFID tags to be packaged are placed, said RFID tag deemed to have passed said functional test.
 5. The method of claim 4 further comprising packaging said RFID tag after said placing.
 6. The method of claim 4 further comprising: transmitting a second wireless signal to a second RFID tag, while said second RFID tag is in the grasp of said machine, to administer a second functional test to said second RFID tag, said second RFID tag having an on-die antenna adapted to receive said second wireless signal; determining that second RFID tag has failed said second functional test; and, placing said second RFID tag in a second distinct location, said second distinct location where scrap RFID tags are placed.
 7. The method of claim 2 wherein said distinct location is where RFID tags to be used are placed, said RFID tag deemed to have passed said functional test.
 8. The method of claim 2 wherein said distinct location is a starting location for a packing process that packages said RFID tag, said RFID tag deemed to have passed said functional test.
 9. The method of claim 2 wherein said distinct location is where RFID tags that are deemed marginally acceptable are placed, said RFID tag deemed to have marginally passed said functional test.
 10. The method of claim 1 wherein said machine is a pick-and-place machine.
 11. The method of claim 10 wherein said transmitting a wireless signal further comprises transmitting a wireless signal from an antenna that is attached to said pick-and-place machine.
 12. The method of claim 10 wherein other RFID tags yet to be picked and that were manufactured from a same wafer that said RFID tag was manufactured from are not functionally tested with said wireless signal, said RFID tag being closer than said other RFID tags to said antenna.
 13. The method of claim 1 wherein other RFID tags yet to be picked and that were manufactured from a same wafer that said RFID tag was manufactured from are not functionally tested with said wireless signal, said RFID tag being closer than said other RFID tags to an antenna that transmits said wireless signal during said administering of said functional test.
 14. The method of claim 1 wherein said RFID tag on-die antenna is electrically isolated from said RFID tag's die seal ring.
 15. The method of claim 1 wherein said RFID tag on-die antenna is electrically integrated with a stacked metallic structure, said stacked metallic structure to thwart penetration of contaminates into said RFID tag's active device area.
 16. The method of claim 15 wherein said stacked metallic structure comprises a wire, a bar contact and a bar via.
 17. An apparatus, comprising: a pick-and-place machine to pick an RFID tag and place said RFID tag at a location, said RFID tag having an on-die antenna; and, an RFID tag functional tester having an antenna, said antenna to transmit a wireless signal used to functionally test said RFID tag while said RFID tag is in the grasp of said pick-and-place machine.
 18. The apparatus of claim 17 wherein said pick-and-place machine places said RFID tag at said location via a trajectory, said RFID tag functional tester being situated independently of said pick-and-place machine and having said antenna situated so as to test said RFID tag while said RFID tag passes a point along said trajectory.
 19. The apparatus of claim 17 wherein said antenna is attached to said pick-and-place machine.
 20. The apparatus of claim 17 wherein said RFID tag on-die antenna is electrically isolated from said RFID tag's die seal ring.
 21. The apparatus of claim 17 wherein said RFID tag on-die antenna is electrically integrated with a stacked metallic structure, said stacked metallic structure to thwart penetration of contaminates into said RFID tag's active device area.
 22. A method, comprising: a) picking an RFID tag from amongst a plurality of RFID tags manufactured from a same wafer, said RFID tag having an on-die antenna; b) transmitting a wireless signal to said RFID tag to administer a functional test to said RFID tag; c) determining that said RFID tag passed said functional test; and, d) packaging said RFID tag.
 23. The method of claim 22 wherein said transmitting a wireless signal further comprises transmitting a wireless signal from an antenna that is attached to a pick-and-place machine that performs said picking.
 24. The method of claim 22 wherein other RFID tags yet to be picked from said sawed wafer are not functionally tested with said wireless signal, said RFID tag being closer than said other RFID tags to an antenna that transmits said wireless signal.
 25. The method of claim 22 wherein said RFID tag on-die antenna is electrically isolated from said RFID tag's die seal ring.
 26. The method of claim 22 wherein said RFID tag on-die antenna is electrically integrated with a stacked metallic structure, said stacked metallic structure to thwart penetration of contaminates into said RFID tag's active device area.
 27. The method of claim 22 where said stacked metallic structure comprises a bar wire and a bar via. 